doc: Add preliminary Raspberry Pi guide

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 - [novaboot-shell](server/novaboot-shell.pod)
 - [adduser-novaboot](server/adduser-novaboot.pod)
+
+### Hardware guides
+
+- [Raspberry Pi](./doc/README.rpi.md) (work-in-progress)

diff --git a/doc/README.rpi.md b/doc/README.rpi.md
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+# Using Novaboot with Raspberry Pi
+
+This document describes how to use Novaboot with Raspberry Pi 4B
+(RPi).
+
+> :warning: This is work in progress.
+
+First, you need to setup the hardware – connect a serial line and
+remote reset. A possible setup can be seen in the figure below.
+
+![RPi setup](./rpi.jpg)
+
+- You need to enable serial port in the bootloader (U-Boot).
+
+  Update rpi-eeprom to the newest version
+
+  Run `rpi-eeprom-config --edit`.
+
+  Change `BOOT_UART` to `1`.
+
+<!-- // Add BOOT_ORDER=0xf12 (see https://www.raspberrypi.com/documentation/computers/raspberry-pi.html#BOOT_ORDER) -->
+
+- Connect USB-TTL-UART converter to the connector pins 8, 9, 10 (TXD0, GND, RXD0).
+
+- Put U-Boot bootloader to the SD card
+
+  Compile U-Boot:
+
+        make rpi_arm64_defconfig
+        make CROSS_COMPILE=aarch64-unknown-linux-gnu- -j8
+        cp u-boot.bin ...
+
+   config.txt - add to `[pi4]` section:
+
+        kernel=u-boot.bin
+        arm_64bit=1
+        enable_uart=1
+
+- Remote reset (and power on/off) can be controlled with an
+  USB-controlled relay connected to pins RUN and GLOBAL_EN.

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